PSI - Issue 14

Afroz Shaikh et al. / Procedia Structural Integrity 14 (2019) 782–789 Afroz Shaikh / Structural Integrity Procedia 00 (2018) 000–000

784

3

Table 1. Chemical composition

Al

V

Fe

O

Sn

Cu

Mo

Ti

Wt %

6.43

4.11

0.14

0.2

<0.04

<0.04

<0.04

Bal

In order to obtain different microstructures, different heat treatment processes were employed, 1. Heat treatment cycle 1 (HT 1): Heating above β transition temperature, followed by different cooling rates (water quenched - WQ, air cooled - AC and furnace cooled - FC). 2. Heat treatment cycle 2 (HT 2): Heating below β transition temperature followed by different cooling rates (WQ, AC and FC). 3. Heat treatment cycle 3 (HT 3): Heating above β transition temperature then furnace cool up to 950 °C and then cooling with different cooling rates (WQ, AC and FC). The details of the heat treatment cycles are presented in Fig. 1. One inch by one inch specimens were prepared for Heat treatment. Heat treatment was carried out in Therlek Box Type muffle furnace. Furnace has a chamber size of 300 mm × 300 mm × 450 mm in which a maximum temperature of 1200 °C can be reached. Furnace has 12 nos. of Silicon carbide heating elements. Heat-treated specimens were etched using Kroll etchant (92 ml H 2 O, 2 ml HF and 6 ml HNO 3 ) for microstructure analysis. Microstructural analysis was done using CARL ZEISS optical microscope with Image Analyzer software Z.2m.

Fig. 1. Different heat treatment cycles (a) HT 1 (b) HT 2 (c) HT 3.

3. Results 3.1. Microstructural analysis

The microstructure of as received material is shown in Fig. 2. Microstructure is of duplex type consisting of primary equiaxed α and transformed β. Volume fraction of α phase is around 75% and that of transformed β is around 25%. Hardness of as received material is 330 HV.

The microstructure obtained after HT 1 is shown in Fig. 3. Water quenched specimen shows acicular ά martensitic microstructure (Fig. 3a-b) whereas a lamellar type of microstructure consisting of acicular α and transformed β with grain boundary α on the prior β grains is obtained after air cooling (Fig. 3c-d). Upon furnace cooling a coarse lamellar (Plate like) type of microstructure consisting of α and β is obtained (Fig. 3e-f).